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PubMed1989

Factors involved in absorption of organic mercuric compounds from rat small intestine: comparative study with mercuric chloride in situ.

A correlation between absorption of organic mercuric compounds and their molecular weight or lipophilicity was investigated by the perfusion of rat small intestine. The intestine was perfused for 1.0 hr at different osmolarity and different pH with buffers containing 10(-4) M organic mercuric compounds, methyl mercuric chloride (MMC), phenyl mercuric chloride (PMC), p-chloromercuribenzoic acid (PCMB) and p-chloromercuriphenylsulfonic acid (PCMBS). The order of absorption of these compounds at several osmolarities and pHs (MMC greater than PMC greater than PCMB greater than PCMBS) was inversely correlated to their molecular weight. The increase in pH decreased markedly the absorption and n-octanol/water partition coefficient of PCMB, and it decreased scarcely those of MMC, PMC and PCMBS. The order of the coefficients at each pH was as follows; PMC greater than MMC greater than PCMB greater than PCMBS, in disagreement with the order of absorption. These results suggest that the molecular weight is more important factor in the intestinal absorption of organic mercuric compounds than the lipophilicity.

Animals↗
PubMed2001

Technical report: mercury in the environment: implications for pediatricians.

Mercury is a ubiquitous environmental toxin that causes a wide range of adverse health effects in humans. Three forms of mercury (elemental, inorganic, and organic) exist, and each has its own profile of toxicity. Exposure to mercury typically occurs by inhalation or ingestion. Readily absorbed after its inhalation, mercury can be an indoor air pollutant, for example, after spills of elemental mercury in the home; however, industry emissions with resulting ambient air pollution remain the most important source of inhaled mercury. Because fresh-water and ocean fish may contain large amounts of mercury, children and pregnant women can have significant exposure if they consume excessive amounts of fish. The developing fetus and young children are thought to be disproportionately affected by mercury exposure, because many aspects of development, particularly brain maturation, can be disturbed by the presence of mercury. Minimizing mercury exposure is, therefore, essential to optimal child health. This review provides pediatricians with current information on mercury, including environmental sources, toxicity, and treatment and prevention of mercury exposure.

Adult↗
PubMed1984

Differential effects of sodium selenite and methylmercury(II) on membrane permeability and DNA replication in HeLa S3 carcinoma cells: a preliminary report regarding the modification of organomercurial toxicity by selenium compounds.

When viewed in terms of their concentration in the growth medium, sodium selenite and methylmercuric hydroxide--administered individually to HeLa S3 cells--are of equal efficacy in inhibiting DNA synthesis: the dose-response curves overlap and 50% residual DNA synthesis occurs at 6.13 microM of either chemical. A different picture, however, emerges if replication is expressed as a function of the actual amounts of toxicant bound per cell. Now, the dose-response curves do not overlap and Na2SeO3 is much more toxic than CH3HgOH: 50% inhibition of DNA replication exists at 5.37 X 10(-17) moles of Se bound per cell and at 3.63 X 10(-15) moles of Hg bound per cell. Further, selenite is taken up by the cells more slowly than methylmercury and its (limiting) cellular concentration is below that of the organomercurial. Lastly, much higher levels of selenite in the growth medium are required to bring about the same degree of membrane damage as the one caused by methylmercury. These differential effects may have a bearing on the observation, well-known but thus far unexplained, that selenite and methylmercury are strikingly less toxic to animals when administered simultaneously than they are when administered individually: selenium may counteract the membrane-destabilizing characteristics of methylmercury and it may retard its binding to the cells. Data on the inhibition of DNA synthesis have been obtained when selenite and methylmercury are administered simultaneously to HeLa S3 cells in varied molar ratios. Best mutual protection appears to exist when the two chemicals are present in equimolar amounts or when there is a slight excess of selenite.

Cell Membrane Permeability↗
PubMed1982

Perspectives on the central nervous system toxicity of methylmercury.

Methylmercury is a widespread and highly toxic environmental pollutant. The source of the substance in the environment is industrial and agricultural use. Chronic methylmercury poisoning is characterized by peripheral and central nervous system damage. The rate of absorption and distribution of this organomercurial into neural tissue determines the rate of development and the severity of the neural lesion. Furthermore, the rate of metabolism and excretion of an organomercurial will greatly influence its neural toxicity. There are differences in the accumulation of methylmercury in different regions of the brain, as well as by the different cell types in these regions. The significance of this variable accumulation of methylmercury is not known. Methylmercury influences a large number of neurocellular functions ranging from inhibition of membrane integrity to alteration in the synthesis and release of transmitter substances.

Animals↗
PubMed1989

The action of organic mercury compounds on the function of isolated mammalian heart muscle.

The effects of four organic mercury compounds (methylmercuric chloride; bromomercurihydroypropane, BMHP; chlormerodrin; p-chloromercuribenzoic acid, PCMB) on mechanical and electrical functions of guinea-pig papillary muscles were investigated. An initial decline in contraction force was followed by a transient positive inotropic response. The first was accompanied by a shortening of the action-potential duration and by a reduction of the depolarization velocity and the duration of the Ca2+-dependent slow response. The latter was characterized by an indirect component (release of noradrenaline) and by a direct component, which was dependent on the stimulation rate and on the extracellular concentration of Na+ and K+. The direct positive effect, therefore, was likely to have resulted from inhibition of the sarcolemmal Na+ + K+-ATPase. This notion was confirmed by experiments with isolated membrane particles. The prevalence of the negative or positive inotropic action of these compounds could be ascribed to their lipophilic or hydrophilic properties, respectively.

Action Potentials↗
PubMed2003

Formal total synthesis of (+)-salicylihalamides A and B: a combined chiral pool and RCM strategy.

The formal total synthesis of the (+)-salicylihalamides A and B is detailed, utilizing a chiral pool approach to generate the three stereogenic centers and a ring-closing metathesis (RCM) for the formation of the macrocyclic ring structure. Starting from a known glucose-derived alcohol, the formal total synthesis was achieved in an efficient 13-step protocol in 26% overall yield. It was found that substitution at the remote phenolic group significantly influenced the ratio of the E- and Z-double bond products in the RCM step. The introduction of phenol protecting groups provided E-isomers preferentially and also enhanced the rates of the RCM reactions.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed2004

Blood organic mercury and dietary mercury intake: National Health and Nutrition Examination Survey, 1999 and 2000.

Blood organic mercury (i.e., methyl mercury) concentrations among 1,709 women who were participants in the National Health and Nutrition Examination Survey (NHANES) in 1999 and 2000 (1999-2000 NHANES) were 0.6 microg/L at the 50th percentile and ranged from concentrations that were nondetectable (5th percentile) to 6.7 microg/L (95th percentile). Blood organic/methyl mercury reflects methyl mercury intake from fish and shellfish as determined from a methyl mercury exposure parameter based on 24-hr dietary recall, 30-day food frequency, and mean concentrations of mercury in the fish/shellfish species reported as consumed (multiple correlation coefficient > 0.5). Blood organic/methyl mercury concentrations were lowest among Mexican Americans and highest among participants who designated themselves in the Other racial/ethnic category, which includes Asians, Native Americans, and Pacific Islanders. Blood organic/methyl mercury concentrations were ~1.5 times higher among women 30-49 years of age than among women 16-29 years of age. Blood mercury (BHg) concentrations were seven times higher among women who reported eating nine or more fish and/or shellfish meals within the past 30 days than among women who reported no fish and/or shellfish consumption in the past 30 days. Blood organic/methyl mercury concentrations greater than or equal to 5.8 microg/L were lowest among Mexican Americans (2.0%) and highest among examinees in the Other racial/ethnic category (21.7%). Based on the distribution of BHg concentrations among the adult female participants in 1999-2000 NHANES and the number of U.S. births in 2000, > 300,000 newborns each year in the United States may have been exposed in utero to methyl mercury concentrations higher than those considered to be without increased risk of adverse neurodevelopmental effects associated with methyl mercury exposure.

Adolescent↗